1. Field of the Invention
The invention relates to a charge control device that controls charging and discharging of a storage battery in which a plurality of storage blocks, each including a plurality of storage elements, are connected in series.
2. Description of the Related Art
As a driving battery or an auxiliary battery for pure electric vehicles, hybrid vehicles, and fuel cell vehicles, a storage battery is available in which a plurality of storage elements are connected in series. In general, a storage battery, such as a secondary battery, does not output sufficient power when the temperature thereof is low. Thus, methods of performing forced continuous charging and discharging to increase the temperature of storage batteries have already been available.
Japanese Patent Application Publication No. 2006-174597 (JP-A-2006-174597) describes a method of rapidly recovering the capacity of a battery by appropriately controlling charging and discharging according to the driving conditions of a vehicle and the amount of electricity remaining in the battery, and accelerating the increase in temperature with the use of the internal heat generation in the battery.
However, the internal resistance of each storage element varies depending on the temperature of the storage element. Specifically, the temperature and the internal resistance of a storage element have a correlation with each other, and as shown in FIG. 6, the internal resistance increases as the temperature of the storage element decreases.
The value of the current flowing through each of the storage elements is the same, and therefore, the amount of voltage reduction during continuous charging or discharging is large in the low-temperature storage element. When the voltage level of a storage element is less than a predetermined value, deterioration progresses, which can reduce the lifetime of the storage battery.
It is possible to identify the storage element in which the amount of voltage reduction is large by providing each of the storage elements with a voltage sensor. However, when this method is used, the number of voltage sensors is large and costs therefore increase.